1. Field of the Invention
The present invention relates to an end mill which is capable of performing an axial cutting and a cross feed cutting with a throw-away tip mounted on a forward end of an end mill body.
2. Related Art Statement
FIGS. 1 and 2 of the accompanying drawings show an example of a conventional end mill in which a single throw-away tip is mounted on a forward end of an end mill body 1. The end mill shown in FIGS. 1 and 2 is arranged such that a throw-away tip 2 of a square shape is detachably mounted on a forward end of the end mill body 1. A cutting edge ridge of the tip 2 located at a forward end thereof and extending from an outer peripheral side of the end mill body 1 toward an inner peripheral side thereof forms an end cutting edge 2a, and a cutting edge ridge extending from an outer peripheral end of the end cutting edge 2a toward a rearward end of the end mill body 1 in the direction of an axis O forms a peripheral cutting edge 2b.
In the end mill described above, the end cutting edge 2a is formed in spaced or offset relation to the axis O, as clearly seen from FIG. 1. This, when an axial cutting is performed on a workpiece, would cause a columnar core, which is a portion of the workpiece remaining uncut, to be formed at a center of rotation, and the core would impinge against the tip 2. Accordingly, the end mill has an inconvenience that it would be incapable of performing the axial cutting.
FIGS. 3 and 4 show another example of a conventional end mill in which an end cutting edge 12a of a throw-away tip 12 is formed so as to extend across an axis O of an end mill body. With such tip 12, no core would be formed at a center of rotation, and it would be possible to perform both an axial cutting and a cross feed cutting.
In the end mill illustrated in FIGS. 3 and 4, however, a cutting speed at a portion of the end cutting edge 12a located adjacent the axis O is extremely low and, furthermore, when the axial cutting is performed, an excessive thrust load is applied to the portion of the end cutting edge 12a. This would cause a problem that the portion of the end cutting edge 12a adjacent the axis O is chipped or fractured. In addition, since the end cutting edge 12a is formed so as to extend across the axis O, the diameter of the end mill is subject to restriction by the size of the throw-away tip 12. In other words, a problem would occur that if the end mill is desired to have an increased diameter, the tip 12 must also have an increased size.